Exhaust gas purification catalysts for treating exhaust gases from automobiles in which a noble metal is supported on or solid-dissolved in an inorganic oxide such as a cerium-based composite oxide, a zirconium-based composite oxide, or a perovskite-type composite oxide are known (Patent Literature 1 to 6). Such catalysts are widely used as catalysts capable of simultaneously removing hydrocarbons (HC), nitrogen oxides (NOX), and carbon monoxide (CO).
The technology for suppressing the poisoning of noble metals (in particular, Pd) with hydrocarbons (HC) by including an alkaline-earth metal sulfate in these catalysts is known.
Conventionally, the catalyst layer in the exhaust gas purification catalyst as described above is formed on a substrate, for example, a cordierite honeycomb substrate, which itself has no exhaust gas purifying ability. However, in recent years, exhaust gas purification catalysts in which a noble metal is supported on a substrate composed of inorganic oxide particles has been proposed (Patent Literature 7).